Complete nucleotide sequence of the genomic RNA of an Amami-O-shima strain of East Asian Passiflora potyvirus

The Generation of Attenuated Mutants of East Asian Passiflora Virus via Deletion and Mutation in the N-Terminal Region of the HC-Pro Gene for Control through Cross-Protection

East Asian Passiflora virus (EAPV) causes passionfruit woodiness disease, a major threat limiting passionfruit production in eastern Asia, including Taiwan and Vietnam. In this study, an infectious cDNA clone of a Taiwanese severe isolate EAPV-TW was tagged with a green fluorescent protein (GFP) reporter to monitor the virus in plants. Nicotiana benthamiana and yellow passionfruit plants inoculated with the construct showed typical symptoms of EAPV-TW. Based on our previous studies on pathogenicity determinants of potyviral HC-Pros, a deletion of six amino acids (d6) alone and its association with a point mutation (F8I, simplified as I8) were conducted in the N-terminal region of the HC-Pro gene of EAPV-TW to generate mutants of EAPV-d6 and EAPV-d6I8, respectively. The mutant EAPV-d6I8 caused infection without conspicuous symptoms in N. benthamiana and yellow passionfruit plants, while EAPV-d6 still induced slight leaf mottling. EAPV-d6I8 was stable after six passages under greenhouse conditions and displayed a zigzag pattern of virus accumulation, typical of a beneficial protective virus. The cross-protection effectiveness of EAPV-d6I8 was evaluated in both N. benthamiana and yellow passionfruit plants under greenhouse conditions. EAPV-d6I8 conferred complete cross-protection (100%) against the wild-type EAPV-TW-GFP in both N. benthamiana and yellow passionfruit plants, as verified by no severe symptoms, no fluorescent signals, and PCR-negative status for GFP. Furthermore, EAPV-d6I8 also provided complete protection against Vietnam's severe strain EAPV-GL1 in yellow passionfruit plants. Our results indicate that the attenuated mutant EAPV-d6I8 has great potential to control EAPV in Taiwan and Vietnam via cross-protection.

Generation of Attenuated Passiflora Mottle Virus Through Modification of the Helper Component Protease for Cross Protection

Passiflora mottle virus (PaMoV), an aphid-borne potyvirus, is the primary causal virus of devastating passionfruit woodiness disease in Vietnam. Here we generated a nonpathogenic, attenuated PaMoV strain for disease control by cross protection. A full-length genomic cDNA of PaMoV strain DN4 from Vietnam was constructed to generate an infectious clone. The green fluorescent protein was tagged at the N-terminal region of the coat protein gene to monitor in planta the severe PaMoV-DN4. Two amino acids within the conserved motifs of helper component protease (HC-Pro) of PaMoV-DN4 were mutated individually or in combination as K53E or/and R181I. Mutants PaMoV-E53 and PaMoV-I181 induced local lesions in Chenopodium quinoa plants, while PaMoV-E53I181 caused infection without apparent symptoms. In passionfruit (Passiflora edulis) plants, PaMoV-E53 elicited severe leaf mosaic and PaMoV-I181 induced leaf mottling, while PaMoV-E53I181 caused transient mottling followed by symptomless recovery. PaMoV-E53I181 was stable after six serial passages in yellow passionfruit (Passiflora edulis f. flavicarpa) plants. Its temporal accumulation levels were lower than those of the wild type, with a zigzag accumulation pattern, typical of a beneficial protective virus. An RNA silencing suppression (RSS) assay revealed that all three mutated HC-Pros are defective in RSS. Triplicated cross-protection experiments with a total of 45 plants showed that the attenuated mutant PaMoV-E53I181 provided a high protection rate (91%) against the homologous wild-type virus in passionfruit plants. This work revealed that PaMoV-E53I181 can be used as a protective virus to control PaMoV by cross protection.

Characterization and Detection of Passiflora Mottle Virus and Two Other Potyviruses Causing Passionfruit Woodiness Disease in Vietnam

Passionfruit plantings in Vietnam increased to 10,000 ha in 2019. However, outbreaks of passionfruit woodiness disease (PWD) have become a serious threat to production. In this study, five virus isolates (DN1, DN4, NA1, GL1, and GL2) were collected from different areas of Vietnam. Their causal roles in PWD were verified by back-inoculation to passionfruit. Analyses of coat protein (CP) and genomic sequences revealed that the GL1 isolate is closely related to East Asia Passiflora virus (EAPV) AO strain of Japan (polyprotein nt and aa identities of 98.1 and 98.2%, respectively), and the GL2 isolate is related to Telosma mosaic virus (TelMV) isolate PasFru, China (polyprotein nt and aa identities of 87.1 and 90.9%, respectively). CP comparison, host range, and cytological characterization indicated that DN1, DN4, and NA1 are potyviruses but are different from EAPV and TelMV. Phylogenic analyses of their CP and genome sequences indicated that these three isolates and the passionfruit severe mottle-associated virus Fujian isolate of China belong to a distinct clade, which does not meet the threshold (76% nt identity of polyprotein) to be regarded as any of potyviral species. Thus, a new species name, Passiflora mottle virus, (PaMoV), has been proposed by the International Committee on Taxonomy of Viruses. A rabbit antiserum was produced against the CP of DN1, and it can distinguish PaMoV from TelMV and EAPV in western blotting and enzyme-linked immunosorbent assay (ELISA) without cross-reactions. Field surveys of 240 samples by ELISA and reverse transcription PCR found that PWD in Vietnam is caused mainly by PaMoV, followed by EAPV, mixed infection of PaMoV and EAPV, and rare cases of TelMV.

Characterization and Distribution of a Potyvirus Associated with Passion Fruit Woodiness Disease in Uganda

This article describes the incidence and etiology of a viral disease of passion fruit in Uganda. Symptoms, including those characteristic of passion fruit woodiness disease (PWD), were observed on 32% of plants in producing areas. Electron microscopic observations of infected tissues revealed flexuous filaments of ca. 780 nm. Enzymelinked immunosorbent assays indicated a serological relationship with Cowpea aphid-borne mosaic virus (CABMV) and Passion fruit ringspot virus (PFRSV). In host range studies, only species in the families Solanaceae and Chenopodiaceae were susceptible, and neither Vigna unguiculata nor Phaseolus vulgaris became infected. Coat protein (CP) gene sequences of eight isolates exhibited features typical of potyviruses and were highly similar (88 to 100% identity). However, the sequences had limited sequence identity with CP genes of two of the three potyviruses reported to cause PWD: East Asian Passiflora virus and Passion fruit woodiness virus (PWV). Deduced amino acid sequences for the CP of isolates from Uganda had highest identity with Bean common mosaic necrosis virus (BCMNV) (72 to 79%, with evolutionary divergence values between 0.17 and 0.19) and CABMV (73 to 76%, with divergence values between 0.21 and 0.25). Based on these results and in accordance with International Committee for Taxonomy of Viruses criteria for species demarcation in the family Potyviridae, we conclude that a previously unreported virus causes viral diseases on passion fruit in Uganda. The name "Ugandan Passiflora virus" is proposed for this virus.

Indigenous and introduced potyviruses of legumes and Passiflora spp. from Australia: biological properties and comparison of coat protein nucleotide sequences

Five Australian potyviruses, passion fruit woodiness virus (PWV), passiflora mosaic virus (PaMV), passiflora virus Y, clitoria chlorosis virus (ClCV) and hardenbergia mosaic virus (HarMV), and two introduced potyviruses, bean common mosaic virus (BCMV) and cowpea aphid-borne mosaic virus (CAbMV), were detected in nine wild or cultivated Passiflora and legume species growing in tropical, subtropical or Mediterranean climatic regions of Western Australia. When ClCV (1), PaMV (1), PaVY (8) and PWV (5) isolates were inoculated to 15 plant species, PWV and two PaVY P. foetida isolates infected P. edulis and P. caerulea readily but legumes only occasionally. Another PaVY P. foetida isolate resembled five PaVY legume isolates in infecting legumes readily but not infecting P. edulis. PaMV resembled PaVY legume isolates in legumes but also infected P. edulis. ClCV did not infect P. edulis or P. caerulea and behaved differently from PaVY legume isolates and PaMV when inoculated to two legume species. When complete coat protein (CP) nucleotide (nt) sequences of 33 new isolates were compared with 41 others, PWV (8), HarMV (4), PaMV (1) and ClCV (1) were within a large group of Australian isolates, while PaVY (14), CAbMV (1) and BCMV (3) isolates were in three other groups. Variation among PWV and PaVY isolates was sufficient for division into four clades each (I-IV). A variable block of 56 amino acid residues at the N-terminal region of the CPs of PaMV and ClCV distinguished them from PWV. Comparison of PWV, PaMV and ClCV CP sequences showed that nt identities were both above and below the 76-77% potyvirus species threshold level. This research gives insights into invasion of new hosts by potyviruses at the natural vegetation and cultivated area interface, and illustrates the potential of indigenous viruses to emerge to infect introduced plants.